Automated and Continuous Redox Potential Measurements in Soil
- Michel Vorenhout *a,
- Harm G. van der Geestc,
- Daan van Marumb,
- Kees Wattelb and
- Herman J. P. Eijsackersa
- a Institute of Ecological Science, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
c Aquatic Ecology and Ecotoxicology, Faculty of Science, University of Amsterdam, Kruislaan 320, 1098 SM, Amsterdam, the Netherlands
b Electronics Department, Faculty of Earth and Life Sciences, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, the Netherlands
Redox potential (Eh) describes the electrical state of a matrix. In soils, Eh is an important parameter controlling the persistence of many organic and inorganic compounds. A popular, but also criticized, manual measuring method makes use of a small tip of Pt placed on a copper wire that is placed in the soil; a reference electrode is placed in the same soil at a fixed distance. Fluctuations in redox potential values measured in the soil can be very large and depth-dependent. This will be overlooked when making single-point measurements. We developed the datalogger Hypnos 2.0 for continuous redox potential and temperature measurements at various depths in the soil and without disturbance of the site. Hypnos is field-deployable, relatively cheap, and runs on batteries. The datalogger can use a “sleep mode” between sampling events. In sleep mode, there is no constant voltage on the Pt wire or the reference electrode, but there is only a short pulse during sampling. We did not measure an effect of this short pulse on the measured redox potential. In sandy soils in mesocosms and in a salt marsh soil we measured changes in the Eh as large as from −400 to +100 mV within 4 d, and daily cycles of 200 mV. Both absolute redox potential values and their diurnal variations were depth-dependent. Because single redox measurements are insufficient in describing redox conditions in some soil systems, Hypnos can be a powerful tool when studying the effects of fluctuating redox conditions on metal availability and pollutant degradation.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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